As a method for producing a metal oxide thin film, a physical method such as a sputtering method, a vacuum evaporation method and the like, and a chemical method such as a CVD method and the like have been conventionally known. However, these methods all have a problem that they require costly apparatus such as a vacuum apparatus or the like.
On the contrary, so-called sol-gel method using a metal alkoxide as a raw material for causing polymerization or crosslinking by hydrolysis and condensation reaction of the raw material has been proposed. However, although such a method is capable of producing an oxide thin film using a relatively economical apparatus, there is a problem that a firing of sol has to be carried out at a high temperature.
As a technique for solving the above-mentioned problems, a method for producing a metal oxide thin film using photoreaction has been examined.
For example, Japanese Kokai Publication Hei-7-187669 discloses a composition containing a substance generating water or an acid by irradiation of light. However, this method is disadvantageous in points that it requires examinations of solubilities of respective components for hydrolysis by water or an acid and that it also requires a high energy beam source such as a low pressure mercury lamp and an excimer laser for decomposing the substance which generates water or an acid.
Japanese Kokai Publication Hei-6-166501 discloses a method for providing photoreactivity by using a β-diketone compound such as acetylacetone, benzoylacetone and the like as an additive. In this method, a curing reaction is supposed to take place attributed to π→π* transition of conjugated electron system characteristic of a metal compound caused by UV rays. However, with respect to a metal compound having no such conjugated system, sufficient reactivity by UV rays cannot be expected. For example, there is a problem that a zinc compound useful as a material for a conductor film and a varistor and a silicon compound useful for an interlayer insulating film cannot be cured.
Among metal oxides, especially compounds having hydrolyzable silyl group such as alkoxyl group containing Si as a metal element are suitable to obtain cured bodies with hardness varying in an extremely wide range covering from hard and fragile properties to soft and elastic properties after being polymerized or crosslinked. Moreover, extremely viscous materials just like grease and sticky materials can also be obtained as the cured bodies. Owing to such properties, compounds having hydrolyzable silyl group can be used widely for industrial uses such as a coating material, grease, a pressure sensitive adhesive, an adhesive, a sealing material, an elastomer, a mold-releasing agent and the like.
However, in the case where a composition containing such a conventionally known compound having hydrolyzable silyl group as described above is used especially as a one-component type adhesive or sealing agent excellent in convenience, since it is made possible to be polymerized or crosslinked by moisture in air, the composition requires to be kept from moisture for storage and it is required to keep the humidity of air constantly low or store the composition in an air-tight container and the like.
Accordingly, such an adhesive or the like is mainly used for a work in a working field where an adhesive sealed in an air-tight container is to be completely consumed within a short time once the container is opened and in the case where storage stability is required due to use in open system for a long duration, for example, in the case of use in a common coating apparatus employed in a production line or the like, stable use of such an adhesive is difficult. That is, in a common coating apparatus, no countermeasure for shutting moisture during the storage and supply of the adhesive is made and there are some types of coating apparatuses which are impossible to shut moisture in terms of the structure.
In order to use an adhesive in a production line, in consideration of line productivity, such a one-component type adhesive in which a compound having a hydrolyzable silyl group and a compound promoting hydrolysis and condensation reaction coexist and therefore which quickly exhibits the adhesive force without requiring mixing is preferable, however such a composition has a problem of inferior storage stability.
When a compound promoting hydrolysis and condensation reaction is selected so as to give a composition excellent in storage stability, there occurs another problem that polymerization or crosslinking reaction cannot be caused quickly in the use.
That is, it has been difficult to obtain a composition which contains a compound having hydrolyzable silyl group and a compound promoting hydrolysis and condensation reaction in form of a one-component liquid and at the same time which is excellent in storage stability and whose polymerization or crosslinking reaction is quickly promoted.
As a technique to solve the above-mentioned problems, a composition which contains a silane compound having an alkoxysilyl or alkylalkoxysilyl group and an aromatic onium salt catalyst and is excellent in storage stability and whose polymerization or crosslinking reaction is quickly promoted is disclosed in Japanese Kokai Publication Sho-53-97098. As reported in “Radiation Curing in Polymer Science and Technology”, (vol 2, Elsevier Applied Science, London, 1993), the technique involves irradiating radiation beam to the aromatic onium salt catalyst for activating the aromatic onium salt catalyst to generate protonic acid from the aromatic onium salt catalyst and promoting hydrolysis and condensation reaction of the alkoxysilyl or alkylalkoxysilyl group by the generated protonic acid. A moisture curable composition containing an onium salt as an acid producing substance capable of promoting moisture-curing of a polymer having alkoxysilyl group is also disclosed in Japanese Kokai Publication 2001-515533 and it is reported that the onium salt shows photosensitivity and isolates an acid immediately after light is irirradiated.
However, an aromatic onium salt catalyst is hardly soluble in a silane compound having alkoxysilyl or alkylalkoxysilyl group and in the case the silane compound is a polymer, the catalyst is particularly inferior in solubility to make a composition opaque, so that the radiation beam hardly penetrate the composition and therefore, crosslinking or curing occurs only in the surface part where the radiation beam is irirradiated and reaction is caused and thus there is a problem that the combination of a hydrolyzable silane and an aromatic onium salt catalyst is limited.
Further, a technique for carrying out photo-crosslinking by combining benzoinsulfonate activated by light rays and a hydrolyzable silane having acryloyl group is disclosed (H. Inoue, et al., J. Photopolym. Sci., vol 12, 129-132, 1999).
Benzoinsulfonate is known as a sensitizer for photopolymerization of acryloyl groups or also a photo-initiator for starting hydrolysis and condensation reaction of the hydrolyzable silyl group. However, photopolymerization of acryloyl groups and hydrolysis and condensation reaction of the hydrolyzable silyl require UV irradiation and irradiation energy for a long time.
Japanese Kokai Publication Hei-6-273936 discloses a photosensitive resin composition containing a polysiloxane polymer obtained by hydrolysis decomposition and partial condensation of a silane compound having hydrolyzable groups and a base generating agent for generating a base by active chemical beam. However, it is generally necessary to heat at 50 to 150° C. after UV irradiation and thus it is difficult to quickly carry out polymerization to a high molecular weight at a room temperature.